Prime mover with recovered energy driven compression of the working fluid

ABSTRACT

A prime mover with recovered energy driven compression for stationary and motor vehicle application. Efficient low compression operation, especially beneficial to small gas turbines, is enabled with either ambient or cryogenic intake air. Two features, exhaust gas recirculation by a jet-compressor and a heat of fusion sink to liquefy motive air to the jet-compressor, decrease regenerative heat exchanger terminal temperature difference relative to turbine temperature drop in low pressure operation while reducing heat exchanger surface area.

CLAIM OF PRIORITY

This Application is a continuation in part of co-pending U.S.Non-Provisional patent application Ser. No. 13/374,861, filed on Jan.20, 2012.

U.S. PATENT DOCUMENTS

U.S. Pat. No. 7,398,841 B2 (2008) Kaufman, Jay S.

OTHER REFERENCES

1. Chrysler Technical Information Office, “History of ChryslerCorporations Gas Turbine Vehicles”, Chrysler Corporation Publication(Jan. 1979)

2. Antoine, H., “Is There a Future For Micro-turbines?, Proceedings ofSecond International Conference on Industrial Gas Turbine Technologies,Bled, Slovenia (April 2004)

3. DeFrate, L. and Hoerl, A. “Optimum Design of Ejectors Using DigitalComputers”, Chemical Engineering Progress, Symposium Series, 21 (1959)

FIELD OF THE INVENTION

The present invention relates to the use of recovered energy to provideminimal compression work in low compression motor vehicle and stationaryengines, and in particular to systems for exhaust gas recirculation by ajet-compressor with liquefaction of the motive fluid by a heat of fusionsink.

BACKGROUND Description of Prior Art

A high efficiency prime mover with renewable energy storage has longbeen a goal of motor vehicle and stationary engine design to provideenergy independence, conserve fossil fuels, and reduce emission ofcombustion products. While the expansion engine of the present inventionis applicable to both reciprocating and rotary engines, it is especiallybeneficial to the gas turbine. The gas turbine offers several advantagesover other engines including simplicity, reliability, low maintenance,low emissions, low weight and ability to burn most any fuel or to run onrecovered heat. It has the potential to provide a universal prime mover,however it is inefficient in the motor vehicle and stationarydistributed electric generation size range, especially with respect tovariable speed operation. This is because of two factors:

-   -   rotor stress limitations imposed by the pressure-speed        relationship, wherein rotor speed is directly proportional to        working fluid flow rate and compression ratio, and indirectly        proportional to rotor diameter    -   high heat exchanger terminal temperature difference relative to        turbine temperature drop.

Both of these factors begin to adversely effect cycle efficiency at apressure ratio less than about 3. As a result turn-down is inefficient,exhaust temperature and rotor stresses are high with rotational speedsexceeding 100,000 rpm, and a large expensive heat exchanger is needed.

Previous efforts to adapt a gas turbine to motor vehicle use, notablythe Chrysler turbine [1] have been unsuccessful. Present efforts toemploy micro-turbines [2] for distributed electric generation areproving successful, but with marginal cost advantage. In general,problems with smaller gas turbine applications are attributable to highcompression work with low density ambient intake air and exhaust gasheat recovery with large and complex regenerative heat exchangers.Several cryogenic compression engines have been built and tested toreduce compression work by, in effect, transferring compression toproduction and storage of liquefied air or nitrogen for compressioncooling. Liquefaction work is by renewable energy or other low costmeans such as off-peak electricity, therefore not chargeable to cycleefficiency. Both Brayton and Rankine cycles, either fired or withfuel-less ambient heating have been tried, however consumption of theliquefied coolant has proved to be excessive and high efficiencyliquefaction is still sought after. Similarly, a highly effectiveregenerative heat exchanger is also sought after. Most gas turbines havea heat exchanger for recovering exhaust heat to improve cycleefficiency. Large surface area and enhanced heat transfer features arecombined to attain high effectiveness. Fixed area recuperatorsconstructed of numerous tubes, brazed or welded in complex headerarrangements and with enhanced heat transfer are difficult tomanufacture and expensive. Another kind of heat exchanger, the rotaryregenerator, attains higher effectiveness than recuperators by providingpassage of the atmospheric and pressurized flow streams, alternatelyover the same heat transfer matrix. Seals to minimize leakage betweenthe streams are difficult to maintain and application is limited to lowcompression systems.

OBJECTS OF THE INVENTION

Accordingly, objects of the prime mover of the present invention are:

-   -   to provide high cycle efficiency in a low compression prime        mover of a transport vehicle drawing ambient atmospheric working        fluid, while utilizing recovery of vehicle braking energy and        other recoverable energy to reduce compression work of the prime        mover;    -   to provide high cycle efficiency throughout the speed range of a        low compression prime mover of a transport vehicle, utilizing        recovery of vehicle braking energy and other recoverable energy        to drive a heat of fusion sink for absorbing heat from and        liquefying the working fluid to reduce compression work of the        prime mover;    -   to provide high cycle efficiency of a low compression prime        mover for distributed electric generation, drawing ambient        atmospheric working fluid, while utilizing recovery of wind,        solar and other recoverable energy to reduce compression work of        the prime mover;    -   to provide high cycle efficiency of a low compression prime        mover for distributed electric generation utilizing recovery of        wind, solar and other recoverable energy to drive a heat of        fusion sink for absorbing heat from and liquefying the working        fluid to reduce compression work of the prime mover;    -   to provide minimal heat transfer surface area of the        regenerative heat exchanger of the prime mover of the present        invention;    -   to provide minimal liquefied working fluid consumption of the        prime mover of the present invention; and    -   to provide a selection of working fluid and heat sink        cryo-coolant combinations for the prime mover of the present        invention.

SUMMARY OF THE INVENTION

The prime mover and associated energy recovery systems of the presentinvention have application in a capacity range of approximately 20 kW(eto 150 kW(e) in which speed of an expansion engine such as a gas turbineis reduced by operation in a compression ratio range of approximately1.1 to 2.5. Problems and deficiencies of the prior art described aboveare improved by the present invention, wherein:

-   -   A feature of the prime mover in accordance with the present        invention lies in providing a jet compressor to circulate        exhaust gas for increasing thermodynamic cycle efficiency in low        compression operation while reducing the size and complexity of        a regenerative heat exchanger;    -   another feature of the prime mover in accordance with the        present invention lies in providing recovered energy available        to a transport vehicle or a distributed electric generator to        drive an ambient primary air compressor to offset motive        compression work of a jet compressor;    -   another feature of the prime mover in accordance with the        present invention lies in providing recovered energy available        to a transport vehicle or a distributed electric generator to        reduce motive compression work of a jet compressor by liquefying        the motive fluid;    -   another feature of the prime mover in accordance with the        present invention lies in providing a heat of fusion sink with a        slush compressor driven by recovered energy to provide suction        pressure for solidifying a melt cryo-coolant during liquefaction        of the working fluid;    -   another feature of the prime mover in accordance with the        present invention lies in providing two parallel working fluid        flow paths, a lower pressure primary working fluid path and a        motive fluid path to minimize consumption of the liquefied        working fluid;    -   another feature of the prime mover in accordance with the        present invention lies in maintaining the melt cryo-coolant of a        heat of fusion sink between a subliming solid-vapor and a liquid        state;    -   another feature of the prime mover in accordance with the        present invention lies in providing on-stream liquefaction of        boiled-off working fluid by circulation through the heat of        fusion sink;    -   another feature of the prime mover in accordance with the        present invention lies in providing partial make-up of the melt        cryo-coolant of a heat of fusion sink by reliquefaction of        vented cryo-coolant in a liquefier powered by recovered energy;    -   another feature of the prime mover in accordance with the        present invention lies in providing make-up of the melt        cryo-coolant of a heat of fusion sink by Dewar exchange; and        still another feature of the prime mover in accordance with the        present invention lies in providing a selection of working fluid        and melt cryo-coolant combinations for economizing coolant        consumption.

Accordingly, the principal object of the present invention is to providea prime mover with high cycle efficiency and economic consumption ofheat sink coolant and liquefied working fluid in vehicle and stationaryapplication. Still further objects and advantages will become apparentfrom a consideration of the ensuing description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention willbecome apparent from the following description when read in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a schematic illustrating a preferred embodiment of a gasturbine engine of the present invention with a recovered energy drivenheat of fusion sink for working fluid liquefaction and compressioncooling.

FIG. 2 is a schematic illustrating a transport vehicle powered by twojet compression gas turbine engines of the present invention withrecovered energy driven compression.

FIG. 2A is a schematic illustrating a preferred embodiment of a jetcompression gas turbine engine of the present invention with recoveredenergy driven compression of ambient atmospheric air.

FIG. 3 is a schematic illustrating an alternate preferred embodiment ofa jet compression gas turbine engine of the present invention with arecovered energy driven heat of fusion sink for working fluidliquefaction and compression cooling.

FIG. 4 is a schematic illustrating an alternate preferred embodiment ofa cryogenic cooling system of the gas turbine engine of the presentinvention with recovered energy driven make-up for evaporated workingfluid and heat sink cryo-coolant.

DESCRIPTION FIGS. 1 to 4

FIG. 1 is a schematic illustrating a preferred embodiment of a gasturbine 100 of the present invention wherein a turbine-generator 102fired from a fueled combustor 104 with a recuperator 106 provideselectrical power to an electrical controller 108 for distribution. Theproducts of combustion 110 of the working fluid continue through theatmospheric side of recuperator 106 and exhaust to atmosphere. A heat offusion sink 112 of a cryogenic cooling system 114 provides liquefactionof a bypass portion of cryogenic intake combustion air 116 drawn throughthe atmospheric side of a chiller 118 by a cryogenic primarymotor-compressor 120. A bypass valve 122 controls the flow of air to theworking fluid side of a freeze Dewar 124 of sink 112. The remainingcombustion air from chiller 118 combines with the liquefied portion froma liquid air Dewar 126 via a liquid air valve 128 to motor-compressor120.

In sink 112, a slush compressor 130 powered by a storage battery 132,circulates nitrogen slush 134 through the shell side of Dewar 124wherein entering frozen nitrogen alternately melts due to heatabsorption from the working fluid and solidifies due to suction pressureof compressor 130. Condensed nitrogen is imported into the shell side ofDewar 124 and nitrogen vapor is vented through a vent 126. Liquefiedworking fluid air 136 for start-up and boil-off replacement is importedto Dewar 126.

An open cycle fired system is selected to illustrate design pointperformance of an 8 kW (10.7 HP) gasoline fired turbine-generator forvehicle or stationary application. Cycle efficiency is 54% at 50,000 rpmwith the turbine compression ratio of 1.5, turbine inlet gas temperatureof 825° C. (1515° F.), air compressor inlet temperature of −172° C.(−280° F.) and recuperator effectiveness of 95%. Under these conditionsfuel consumption is 33 km/L 1.2 kg/hr (2.7 lb/hr), liquefied airconsumption is 44 kg/hr (97 lb/hr) and excess air ratio is 24. Forcomparison a typical reciprocating engine in the same application has acycle efficiency of 18% at 5,000 rpm and compression ratio of 10, andefficiency of a typical micro-turbine is 28% at 96,000 rpm with acompression ratio of 3.6.

The sink is filled with solidified nitrogen and maintained below theboiling point of −196° C. (−325° F.). Reduction of vapor pressure from0.7 to 0.1 atmospheres by the suction compressor provides circulation ofthe alternately melting and solidifying nitrogen. Work input to theslush compressor is 2.6 kW (3.5 HP), requiring recovered energy equal to33% of turbine-generator shaft power. A continuous and sufficient supplyof liquefied air is maintained as recovered energy charges the batteryto drive the slush compressor.

A small [28 kWe (21 HP) peak] recuperated gas turbine, which can bemodified to incorporate cryogenic features of the present invention, isavailable from the Capstone Corporation of Chatsworth, Calif. Cryogeniccomponents including chiller, compressor and Dewar are available fromChart Industries of Garfield Heights, Ohio, Barber-Nichols of Arvada,Co. and Technifab Products of Brazil, Indiana, respectively.

FIG. 2 is a side elevation view illustrating a preferred embodiment of atransport vehicle 240 of the present invention with propulsion providedto two motorized wheels 242 by two 4 Kwe (5.4 HP) jet compression gasturbines 200. An electrical controller 208 distributes recovered energyfrom a storage battery 232, charged by a braking generator 244 forpressurization of the gas turbines 200. A regenerative braking system,which can be adapted to the vehicle of the present invention, isavailable from the Ford Motor Company of Dearborn, Mich.

FIG. 2A is a schematic illustrating a preferred embodiment of a gasturbine 200 of the present invention wherein a turbine-generator 202fired from a fueled combustor 204 with a recuperator 206 provideselectrical power to an electrical controller 208 for distribution. Theworking fluid of gas turbine 200 consists of a motive combustion airportion 246 which drives a jet compressor 248, a circulated exhaustportion 250 which is entrained into the motive air, and an emissionportion 210 which continues to atmosphere through recuperator 206. Amotive compressor 252 provides combustion air through recuperator 206 toa motive nozzle 254 which entrains the circulated exhaust, under controlof an exhaust valve 256, for delivery through a discharge nozzle 258 tocombustor 204.

An open cycle fired system is selected to illustrate performance of agasoline fired gas turbine as prime mover in a compact car operating atan 80 km/hr (50 mph) design point requiring 8 kW (10.7 HP). Compressionwork, normally provided by turbine-generator output, is supplemented by33% recovered vehicle braking energy. Cycle efficiency is 44% at 50,000rpm with motive compression ratio of 5, turbine inlet gas temperature of825° C. (1515° F.), air compressor inlet temperature of 20° C. (68° F.)and recuperator effectiveness of 95%. Under these conditions fueleconomy is 33 km/L (78 mpg) and excess air ratio is 22. High excess airratio associated with the low turbine pressure ratio obviates the effectof combustion products in the recirculating suction flow. For comparisona typical reciprocating engine in the same application has a cycleefficiency of 18% at 5,000 rpm and compression ratio of 10, andefficiency of a typical micro-turbine is 28% at 96,000 rpm with acompression ratio of 3.6.

FIG. 3 is a schematic illustrating an alternate preferred embodiment 300of gas turbine 200 of vehicle 201 (FIG. 2), in which the working fluidis cooled to cryogenic temperature by a heat of fusion sink 306 of acryogenic cooling system 314. The sink 306 is powered by recoveredbraking energy of vehicle 201 (FIG. 2). A turbine-generator 302 firedfrom a fueled combustor 304 with a recuperator 306 provides electricalpower to an electrical controller 308 for distribution. The workingfluid of gas turbine 300 consists of a combustion air portion 316following two parallel flow paths, a circulated exhaust portion 350which is entrained into the motive air, and an emission portion 310which continues to atmosphere through recuperator 306. The firstcombustion air path provides primary air from a cryogenicmotor-compressor 320, drawing air through the atmospheric side of achiller 318 and discharging to combustor 304 via recuperator 306. Thesecond path provides motive air, which is drawn through chiller 318 anda bypass valve 322 for liquefaction and storage in a liquid air Dewar326. The liquid is discharged, as required, back through chiller 318 torecuperator 306 by a motive pump 352 to a jet compressor 348. A motivenozzle 354 entrains the circulated exhaust into the motive air, undercontrol of an exhaust valve 356, for delivery through a discharge nozzle358 to combustor 304.

In sink 312, a slush compressor 330 powered by a battery 332, circulatesa two phase melt cryo-coolant 334 through the shell side of freeze Dewar324 wherein entering cryo-coolant alternately melts due to heatabsorption and solidifies due to suction pressure of compressor 330.Condensed melt cryo-coolant is imported into the shell side of Dewar 324and liquefied air is imported into Dewar 326 for boil-off replacement.

An open cycle fired system is selected to illustrate performance of agasoline fired gas turbine as prime mover in a compact car operating atan 80 km/hr (50 mph) design point requiring 8 kW (10.7 HP). Compressionwork for combustion air is provided by turbine-generator output andcryo-coolant compression work is provided by recovered vehicle brakingenergy, which is limited to 33% of turbine-generator shaft power. Cycleefficiency is 70% at 46,000 rpm with primary air compression ratio of1.4, motive compression ratio of 20, turbine inlet gas temperature of825° C. (1515° F.), air compressor inlet temperature of −172° C. (−280°F.) and recuperator effectiveness of 95%. Under these conditions fueleconomy is 60 km/L (140 mpg), liquefied air consumption is 40 kg/hr (88lb/hr) and excess air ratio is 27. High excess air ratio associated withthe low turbine pressure ratio obviates the effect of combustionproducts in the recirculating suction flow. For comparison a typicalreciprocating engine in the same application has a cycle efficiency of18% at 5,000 rpm and compression ratio of 10, and efficiency of atypical micro-turbine is 28% at 96,000 rpm with a compression ratio of3.6.

The sink is filled with solidified nitrogen coolant and maintained atbelow the boiling point of −196° C. (−325° F.). Reduction of vaporpressure from 0.7 to 0.1 atmospheres by the slush compressor providescirculation of the melting and solidifying nitrogen. Recovered vehiclebraking energy to the slush compressor is 2.4 kW (3.2 HP), equal to 30%of turbine-generator shaft power, while the freeze Dewar providesrequired working fluid reliquefaction of 35 kg/hr (76 lb/hr). Acontinuous and sufficient supply of liquefied air is maintained asrecovered energy charges the battery to drive the slush compressor. Ahigh temperature jet compressor suitable for exhaust gas recirculationin the present invention is available from the Fox Company of Dover,N.J. Other components to enable features of the present invention areavailable as listed for FIG. 1 above.

FIG. 4 is a schematic illustrating an alternate preferred embodiment ofa cryogenic cooling system 414 of gas turbine 300 (FIG. 3), in whichboil-off vapor of the working fluid air and vented nitrogen cryo-coolantis made-up. A boil-off compressor 458 powered by recovered brakingenergy of vehicle 201 (FIG. 2) returns the evaporated working fluid tothe tube side of Dewar 424 for reliquefaction. Vented melt cryo-coolantis made-up with solidified nitrogen by removal and replacement of Dewar424 at flanges 460. Supplementary liquefied nitrogen is provided by abraking energy driven reliquefier 462 powered from a controllar 428. Thevent rate for solidified nitrogen cryo-coolant is estimated at 12%,sufficient for a 100 kg (205 lb) initial inventory to provide 16 hoursof vehicle operation at 80 km/hr (50 mph).

SUMMARY, RAMIFICATIONS AND SCOPE

Accordingly, it is shown that the recovered energy driven compressionengine of this invention improves cycle thermal efficiency in both motorvehicle and stationary application. In particular, it overcomes problemsof the gas turbine in small low pressure applications.

Although the description above contains many specific details, theseshould not be construed as limiting the scope of the invention but asmerely providing illustration of some of the preferred embodiments ofthis invention. For example, turbines, either radial or axial typeshaving either electrical or mechanical output, can be connected inseries to lower expansion ratio and speed, or connected in parallel toincrease power. In addition, the motive compressor, motive pump, primarycompressor and liquefier may be powered by recovered energy of vehiclebraking or draft loss, as well as by solar radiation and wind. Theheating source may be solar radiation as well as combustion in eitheropen or closed working fluid systems. The heat of fusion sink may absorbcompression heat from within the compressor and from the compressoroutlet, as well as absorbing heat from the working fluid at thecompressor inlet.

Thus the scope of the invention should be determined by the appendedclaims and their legal equivalents, rather than by the examples given.

I claim:
 1. The compression means of an expansion engine comprisingcompression cooling means for absorbing heat from said compressionmeans, wherein power is supplied to said cooling means from energystorage means charged by recovered energy selected from the groupconsisting of motion of a transport vehicle, solar radiation and wind.2. The cooling means of claim 1 comprising heat of fusion sink means,wherein cryogenic coolant alternately melts during absorption of heatfrom said compression means and solidifies due to suction pressureinduced by suction means of said sink, at less than the working fluidintake temperature to said compression means.
 3. The storage means ofclaim 2 comprising a storage battery and an electric generator selectedfrom the group consisting of photo voltaic panels and electromagneticrotating machines, wherein said battery, charged by said generator,supplies power to drive said suction means.
 4. The cooling means ofclaim 2 comprising condensed working fluid and melting cryogeniccoolant, wherein the working fluid and the coolant are selected from thegroup consisting of nitrogen, air, nitric oxide, argon, neon, methaneand hydrogen.
 5. A transport vehicle comprising recovered energy storagemeans and exhaust gas circulation means, wherein said storage meanssupplies power to compression means of the vehicle prime mover fordriving said circulation means to circulate exhaust working fluid fromthe expansion means to the heat source means of said prime mover.
 6. Thecirculation means of claim 5 comprising jet compression means, wherein amotive fluid portion of working fluid from said compression meansentrains a portion of exhaust working fluid while discharging the mixedmotive fluid and exhaust working fluid to said heat source means.
 7. Theheat source means of claim 6 comprising regenerative heating means,wherein the vented portion of exhaust working fluid heats the intakeworking fluid from said compression means.
 8. The compression means ofclaim 7 comprising motive fluid liquefaction means, wherein cryogenicworking fluid is liquefied by transfer of heat to melting cryogeniccoolant in heat of fusion sink means of said liquefaction means whileintake working fluid, is cryogenically cooled in regenerative coolingmeans of said liquefaction means.
 9. The sink means of claim 8comprising motive fluid heat absorption means and coolant suction means,wherein the cryogenic coolant alternately melts during absorption ofheat from the cryogenic working fluid in said absorption means, andsolidifies due to suction pressure induced by said suction means. 10.The storage means of claim 9 comprising recovered energy charging means,wherein said storage means is charged by recovered energy selected fromthe group consisting of motion of a transport vehicle and solarradiation.
 11. The charging means of claim 10 comprising a storagebattery and an electric generator selected from the group consisting ofphoto voltaic panels and electromagnetic rotating machines, wherein saidbattery, charged by said generator, supplies power to drive said suctionmeans.
 12. The cooling means of claim 11 comprising condensed workingfluid and cryogenic coolant import means, wherein the working fluid andthe coolant are selected from the group consisting of nitrogen, air,nitric oxide, argon, neon, methane and hydrogen.
 13. The liquefactionmeans of claim 12 comprising boil off gas liquefaction means, whereinexcess vaporized working fluid is reliquefied and returned to saidstorage means.
 14. The prime mover of claim 13 comprising a regenerativegas turbine.
 15. A gas turbine prime mover of a transport vehiclecomprising a cryogenic cooling system for absorbing heat from acryogenic compressor of said prime mover, wherein power is supplied tosaid cooling system from an energy storage system charged by recoveredbraking energy of said vehicle.
 16. The cooling system of claim 15comprising a heat of fusion sink, wherein cryogenic coolant alternatelymelts during absorption of heat from said compressor and solidifies dueto suction pressure induced by a suction compressor of said sink, atless than the working fluid intake temperature to said compressor. 17.The sink of claim 16 comprising a cryogenic coolant replacement systemselected from the group consisting of importation of solidified coolantto said vehicle and liquefaction of coolant on said vehicle, whereinevaporated coolant is periodically replaced with condensed coolant. 18.The storage system of claim 16 comprising a storage battery and anelectric generator, wherein said battery, charged by said generator,supplies power to drive said compressor.
 19. The prime mover of claim 15comprising a jet compressor, wherein a motive fluid portion of workingfluid from said cryogenic compressor entrains a portion of exhaustworking fluid while discharging the mixed motive fluid and exhaustworking fluid to a combustor of said prime mover.
 20. The prime mover ofclaim 18 comprising a working fluid bypass with a bypass compressor anda cryogenic regenerator, wherein a bypass portion of the working fluidcontinues in parallel flow relation with the motive fluid to saidcombustor while regeneratively heating the pressurized motive fluid.